Ionospheric convection response to slow, strong variations in a northward interplanetary magnetic field: A case study for January 14, 1988

Abstract

We analyze ionospheric convection pat terns over the polar regions during the passage of an interplanetary magnetic cloud on January 14, 1988, when the interplanetary magnetic field (IMF) rotated slowly in direction and had a large amplitude. Using the assirnilative mapping of ionospheric electrodynamics (AMIE) procedure, we combine simultaneous observations of ionospheric drifts and magnetic perturbations from many different instruments into consistent patterns of high-latitude electrodynamics, focusing on the period of northward IMF. By combining satellite data with ground-based observations, we have generated one of the most comprehensive data sets yet assembled and used it to produce convection maps for both hemispheres. We present evidence that a lobe convection cell was embedded within normal merging convection during a period when the IMF By and B, components were large and positive. As the IMF became predominantly northward, a strong reversed convection pattern (afternoon-to-morning potential drop of around 100 kV) appeared in the southern (

Multi-site observations of the association between aurora and plasma convection in the cusp/polar cap during a southeastward(<i>B<sub>y</sub></i> <u>~</u> |<i>B<sub>z</sub></i>|) IMF orientation

“…1). Related to this we note that it has been documented previously that during large, continuous southward IMF rotations, a greater qualitative change in the convection pattern occurs at |B y | |B z | (clock angle 135 • ) than at the transition through B z = 0 (Knipp et al, 1993) (see also Freeman et al, 1993;Huang et al, 2000). The corresponding change in auroral configuration at midday (meridian scanning photometer data only) and associated ground magnetic deflection, very similar to that which occurred in the present case, is seen in the two case studies reported by Sandholt and Farrugia (1999).…”

“…There is now increasing evidence supporting the view that plasma convection at dayside high latitudes under conditions of a dominant B y component consists of a composite pattern of so-called merging and lobe convection cells (Reiff and Burch, 1985;Knipp et al, 1993;Lu et al, 1994;Weiss et al, 1995;Crooker et al, 1998;Weimer, 2001;Eriksson et al, 2002). While the merging cells are characterized by the transfer of magnetic flux across the open-closed field line boundary (OCFLB) in the cusp region, the lobe cells circulate plasma in the polar cap region, entirely poleward of the OCFLB.…”

Interhemispheric observations of dayside convection under northward IMF

“…Using quasi-simultaneous interhemispheric measurements on January 14, 1988, Knipp et al [1993] did not observe reverse convection cells in the northern (winter) hemisphere. During this period, there was a positive IMF B X which increasingly favored the southern hemisphere, while in the present study, the IMF B X was negative, which may have allowed for some merging between the IMF and lobe field lines in the northern hemisphere.…”

Hemispheric asymmetries in ionospheric electrodynamics during the solar wind void of 11 May 1999

“…We terns for the mapping. ACE Level 2 Solar Wind data were provided also know from previous work [Knipp et al, 1993] …”

“…The theory also implies that significant interhemispheric differences can develop as the result of dipole tilting. During extreme situations, such as the one we discuss here, the convection may develop into a round/crescent structuring or collapse to a single-cell in one hemisphere and a weak irregular convection system in the other hemisphere, especially if large conductivity asymmetries are present [Knipp et al, 1993 [Richmond and Kamide, 1988]. Typically the procedure is run with 5 to 30 min time resolution producing snapshots of ionospheric convection, currents and conductance to study high-latitude disturbances in the geo-space environment.…”